如何在 pyqt 中实现桌面歌词

前言

酷狗、网抑云和 QQ 音乐都有桌面歌词功能，这篇博客也将使用 pyqt 实现桌面歌词功能，效果如下图所示：

代码实现

桌面歌词部件 LyricWidget 在 paintEvent 中绘制歌词。我们可以直接使用 QPainter.drawText 来绘制文本，但是通过这种方式无法对歌词进行描边。所以这里更换为 QPainterPath 来实现，使用 QPainterPath.addText 将歌词添加到绘制路径中，接着使用 Qainter.strokePath 进行描边，Qainter.fillPath 绘制歌词，这里的绘制顺序不能调换。

对于歌词的高亮部分需要特殊处理，假设当前高亮部分的宽度为 w，我们需要对先前绘制歌词的 QPainterPath 进行裁剪，只留下宽度为 w 的部分，此处通过 QPainterPath.intersected 计算与宽度为 w 的矩形路径的交集来实现裁剪。

对于高亮部分的动画，我们既可以使用传统的 QTimer，也可以使用封装地更加彻底的 QPropertyAnimation 来实现（本文使用后者）。这里需要进行动画展示的是高亮部分，也就是说我们只需改变“高亮宽度”这个属性即可。PyQt 为我们提供了 pyqtProperty，类似于 python 自带的 property，使用 pyqtProperty 可以给部件注册一个属性，该属性可以搭配动画来食用。

除了高亮动画外，我们还在 LyricWidget 中注册了滚动动画，用于处理歌词长度大于视口宽度的情况。

# coding:utf-8
from PyQt5.QtCore import QPointF, QPropertyAnimation, Qt, pyqtProperty
from PyQt5.QtGui import (QColor, QFont, QFontMetrics, QPainter, QPainterPath,
                         QPen)
from PyQt5.QtWidgets import QWidget

config = {
    "lyric.font-color": [255, 255, 255],
    "lyric.highlight-color": [0, 153, 188],
    "lyric.font-size": 50,
    "lyric.stroke-size": 5,
    "lyric.stroke-color": [0, 0, 0],
    "lyric.font-family": "Microsoft YaHei",
    "lyric.alignment": "Center"
}

class LyricWidget(QWidget):
    """ Lyric widget """

    def __init__(self, parent=None):
        super().__init__(parent=parent)
        self.setAttribute(Qt.WA_TranslucentBackground)
        self.lyric = []
        self.duration = 0
        self.__originMaskWidth = 0
        self.__translationMaskWidth = 0
        self.__originTextX = 0
        self.__translationTextX = 0

        self.originMaskWidthAni = QPropertyAnimation(
            self, b'originMaskWidth', self)
        self.translationMaskWidthAni = QPropertyAnimation(
            self, b'translationMaskWidth', self)
        self.originTextXAni = QPropertyAnimation(
            self, b'originTextX', self)
        self.translationTextXAni = QPropertyAnimation(
            self, b'translationTextX', self)

    def paintEvent(self, e):
        if not self.lyric:
            return

        painter = QPainter(self)
        painter.setRenderHints(
            QPainter.Antialiasing | QPainter.TextAntialiasing)

        # draw original lyric
        self.__drawLyric(
            painter,
            self.originTextX,
            config["lyric.font-size"],
            self.originMaskWidth,
            self.originFont,
            self.lyric[0]
        )

        if not self.hasTranslation():
            return

        # draw translation lyric
        self.__drawLyric(
            painter,
            self.translationTextX,
            25 + config["lyric.font-size"]*5/3,
            self.translationMaskWidth,
            self.translationFont,
            self.lyric[1]
        )

    def __drawLyric(self, painter: QPainter, x, y, width, font: QFont, text: str):
        """ draw lyric """
        painter.setFont(font)

        # draw background text
        path = QPainterPath()
        path.addText(QPointF(x, y), font, text)
        painter.strokePath(path, QPen(
            QColor(*config["lyric.stroke-color"]), config["lyric.stroke-size"]))
        painter.fillPath(path, QColor(*config['lyric.font-color']))

        # draw foreground text
        painter.fillPath(
            self.__getMaskedLyricPath(path, width),
            QColor(*config['lyric.highlight-color'])
        )

    def __getMaskedLyricPath(self, path: QPainterPath, width: float):
        """ get the masked lyric path """
        subPath = QPainterPath()
        rect = path.boundingRect()
        rect.setWidth(width)
        subPath.addRect(rect)
        return path.intersected(subPath)

    def setLyric(self, lyric: list, duration: int, update=False):
        """ set lyric

        Parameters
        ----------
        lyric: list
            list contains original lyric and translation lyric

        duration: int
            lyric duration in milliseconds

        update: bool
            update immediately or not
        """
        self.lyric = lyric or [""]
        self.duration = max(duration, 1)
        self.__originMaskWidth = 0
        self.__translationMaskWidth = 0

        # stop running animations
        for ani in self.findChildren(QPropertyAnimation):
            if ani.state() == ani.Running:
                ani.stop()

        # start scroll animation if text is too long
        fontMetrics = QFontMetrics(self.originFont)
        w = fontMetrics.width(lyric[0])
        if w > self.width():
            x = self.width() - w
            self.__setAnimation(self.originTextXAni, 0, x)
        else:
            self.__originTextX = self.__getLyricX(w)
            self.originTextXAni.setEndValue(None)

        # start foreground color animation
        self.__setAnimation(self.originMaskWidthAni, 0, w)

        if self.hasTranslation():
            fontMetrics = QFontMetrics(self.translationFont)
            w = fontMetrics.width(lyric[1])
            if w > self.width():
                x = self.width() - w
                self.__setAnimation(self.translationTextXAni, 0, x)
            else:
                self.__translationTextX = self.__getLyricX(w)
                self.translationTextXAni.setEndValue(None)

            self.__setAnimation(self.translationMaskWidthAni, 0, w)

        if update:
            self.update()

    def __getLyricX(self, w: float):
        """ get the x coordinate of lyric """
        alignment = config["lyric.alignment"]
        if alignment == "Right":
            return self.width() - w
        elif alignment == "Left":
            return 0

        return self.width()/2 - w/2

    def getOriginMaskWidth(self):
        return self.__originMaskWidth

    def getTranslationMaskWidth(self):
        return self.__translationMaskWidth

    def getOriginTextX(self):
        return self.__originTextX

    def getTranslationTextX(self):
        return self.__translationTextX

    def setOriginMaskWidth(self, pos: int):
        self.__originMaskWidth = pos
        self.update()

    def setTranslationMaskWidth(self, pos: int):
        self.__translationMaskWidth = pos
        self.update()

    def setOriginTextX(self, pos: int):
        self.__originTextX = pos
        self.update()

    def setTranslationTextX(self, pos):
        self.__translationTextX = pos
        self.update()

    def __setAnimation(self, ani: QPropertyAnimation, start, end):
        if ani.state() == ani.Running:
            ani.stop()

        ani.setStartValue(start)
        ani.setEndValue(end)
        ani.setDuration(self.duration)

    def setPlay(self, isPlay: bool):
        """ set the play status of lyric """
        for ani in self.findChildren(QPropertyAnimation):
            if isPlay and ani.state() != ani.Running and ani.endValue() is not None:
                ani.start()
            elif not isPlay and ani.state() == ani.Running:
                ani.pause()

    def hasTranslation(self):
        return len(self.lyric) == 2

    def minimumHeight(self) -> int:
        size = config["lyric.font-size"]
        h = size/1.5+60 if self.hasTranslation() else 40
        return int(size+h)

    @property
    def originFont(self):
        font = QFont(config["lyric.font-family"])
        font.setPixelSize(config["lyric.font-size"])
        return font

    @property
    def translationFont(self):
        font = QFont(config["lyric.font-family"])
        font.setPixelSize(config["lyric.font-size"]//1.5)
        return font

    originMaskWidth = pyqtProperty(
        float, getOriginMaskWidth, setOriginMaskWidth)
    translationMaskWidth = pyqtProperty(
        float, getTranslationMaskWidth, setTranslationMaskWidth)
    originTextX = pyqtProperty(float, getOriginTextX, setOriginTextX)
    translationTextX = pyqtProperty(
        float, getTranslationTextX, setTranslationTextX)

上述代码对外提供了两个接口 setLyric(lyric, duration, update) 和 setPlay(isPlay)，用于更新歌词和控制歌词动画的开始与暂停。下面是一个最小使用示例，里面使用 Qt.SubWindow 标志使得桌面歌词可以在主界面最小化后仍然显示在桌面上，同时不会多出一个应用图标（Windows 是这样，Linux 不一定）：

class Demo(QWidget):

    def __init__(self):
        super().__init__(parent=None)
        # 创建桌面歌词
        self.desktopLyric = QWidget()
        self.lyricWidget = LyricWidget(self.desktopLyric)

        self.desktopLyric.setAttribute(Qt.WA_TranslucentBackground)
        self.desktopLyric.setWindowFlags(
            Qt.FramelessWindowHint | Qt.SubWindow | Qt.WindowStaysOnTopHint)
        self.desktopLyric.resize(800, 300)
        self.lyricWidget.resize(800, 300)

        # 必须有这一行才能显示桌面歌词界面
        self.desktopLyric.show()

        # 设置歌词
        self.lyricWidget.setLyric(["Test desktop lyric style", "测试桌面歌词样式"], 3000)
        self.lyricWidget.setPlay(True)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    w = Demo()
    w.show()
    app.exec_()

后记

至此关于桌面歌词的实现方案已经介绍完毕，完整的播放器界面代码可参见：https://github.com/zhiyiYo/Groove，以上~~